This invention relates generally to power semiconductor devices, and more particularly the invention relates to a Schottky diode device and a method of making same.
Power semiconductor rectifiers have a variety of applications including use in power supplies and power converters. Heretofore, Schottky diodes have been used in these applications. A Schottky diode is characterized by a low turn-on voltage, fast turnoff, and nonconductance when the diode is reverse biased. To create a Schottky diode a metal-silicon barrier must be formed. In order to obtain the proper characteristics for the Schottky diode, the barrier metal is likely different than the metal used in other process steps such as metal ohmic contacts.
Copending application serial No. 09/283,537, incorporated herein by reference, discloses a vertical semiconductor power rectifier device which employs a large number of parallel connected cells, each comprising a MOSFET structure with a gate-to-drain short via common metalization and an associated Schottky diode. This provides a low Vf path through the channel regions of the MOSFET cells to the source region on the other side of the device. The method of manufacturing the rectifier device provides highly repeatable device characteristics at reduced manufacturing costs.
Copending applications Ser. No. 09/620,074 and Ser. No. 09/620,653, supra, effectively increase diode surface by providing a trenched surface on which Schottky material is deposited. The resulting structure has increased current capacity for semiconductor chip area. In accordance with the method of fabricating the Schottky diode, a guard ring is formed around a device region in a semiconductor chip surface. The guard ring has conductivity type opposite to that of the chip body. Using photoresist masking and etching, a plurality of trenches are etched in the surface of the device region, thereby effectively increasing the active surface area in the device region. A Schottky metal is then deposited over the device region in the trenches, and electrode material is deposited to form top and bottom electrodes for the Schottky diode.
To provide for higher reverse breakdown voltage and lower reverse leakage current, a P-N junction can be formed at or near the bottom of the trench surfaces so that when the Schottky diode is reversed biased, a charge depletion region spreads across and spaced-from the trench surface, thereby increasing the reverse breakdown voltage and reducing reverse leakage current. In accordance with a preferred embodiment, the PN junction is formed by ion implantation in alignment with the trench walls. A photoresist mask can be employed to define the ion implanted surface area. Alternatively, an oxide layer can be selectively formed on the surfaces of the trench surface to limit the implantation of ions.
The present invention is directed to an improved method of manufacturing a Schottky rectifier device and the resulting structure.
In accordance with the invention, the effective surface area of a Schottky diode is increased by providing a trenched surface on which Schottky material is deposited. The resulting structure has increased current capacity for semiconductor chip area.
To provide for higher reverse breakdown voltage and lower reverse leakage current, a P-N junction can be formed at or near the bottom of the trench surfaces so that when the Schottky diode is reversed biased, a charge depletion region spreads across and spaced-from the trench surface, thereby increasing the reverse breakdown voltage and reducing reverse leakage current. In accordance with a preferred embodiment, the PN junction is formed by ion implantation in alignment with the trench walls. A photoresist mask can be employed to define the ion implanted surface area. Alternatively, an oxide layer can be selectively formed on the surfaces of the trench surface to limit the implantation of ions.
In accordance with a feature of the invention, the top portions of the trenched surface are doped whereby the Schottky material forms ohmic contacts thereto and Schottky contacts to the side surfaces of the trenches. The ohmic contacts increase forward current and reduce forward voltage of the Schottky diode. Electrode material is then deposited to form top and bottom electrodes for the Schottky diode.